Steam Turbine Power Plant

ABSTRACT

A steam turbine power plant includes heat-source equipment that heats a low-temperature flow by applying a heat medium and thus generates a high-temperature flow, a steam generator using the high-temperature flow generated by the heat-source equipment, a steam turbine driven by the steam generated by the steam generator, an electric generator that converts rotational motive power of the steam turbine into electric power, a heat-medium controller that controls a supply rate of the heat medium supplied to the heat source equipment, a low-temperature flow controller that controls a supply rate of the low-temperature flow supplied to the heat-source equipment, a prediction device that predicts startup constraints of the steam turbine from control input variables of the controllers when the steam turbine is started, and a control input variables setter so as to prevent data predictions by the prediction device from exceeding limit values of startup constraints.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to steam turbine power plants.

2. Description of the Related Art

It is being demanded that a starting time of a steam turbine power plantbe further reduced for suppressed instability of the electric power in agrid-connected power system by connecting renewable energy, representedby wind power generation or solar power generation, to the power system.When the steam turbine is started up, however, steam abruptly increasesin both temperature and flow rate. A consequential sudden increase in asurface temperature of the turbine rotor relative to an internaltemperature thereof augments a radial temperature gradient and thusincreases a thermal stress. An excessive thermal stress could shorten alife of the turbine rotor. In addition, if the change in the temperatureof the steam is significant, differential thermal expansion due to adifference in heat capacity occurs between the rotor and casing of theturbine. If the differential thermal expansion increases, this couldlead to contact between the rotating turbine rotor and the stationarycasing, and hence to damage to both thereof. Accordingly, a startingstate of the steam turbine needs to be controlled to prevent the thermalstress of the turbine rotor and the differential thermal expansionthereof with respect to that of the casing from exceeding respectivemaximum permissible levels (refer to Japanese Patent No. 4723884, shownas Patent Document 1 below, and JP-2009-281248-A, shown as PatentDocument 2 below).

SUMMARY OF THE INVENTION

In Patent Documents 1, 2, however, the flow rate of the steam suppliedto the steam turbine is controlled by a control valve to regulate thethermal stress and the differential thermal expansion, so the thermalstress and the differential thermal expansion are only regulated in arange that the control valve can control the flow rate of the steam.Another problem exists with energy efficiency since surplus steam isgiven away via a bypass valve for reduced supply of the steam to thesteam turbine.

The present invention has been made with the above in view, and anobject of the invention is to provide a steam turbine power plantadapted to start operating very efficiently in an extended control rangeof its startup constraints such as a thermal stress.

In order to attain the above object, the present invention includes heatsource equipment that heats a low-temperature flow by applying a heatmedium to generate a high-temperature flow, a steam generator thatgenerates steam using the high-temperature flow generated by the heatsource equipment, a steam turbine driven by the steam generated by thesteam generator, an electric generator that converts rotational motivepower of the steam turbine into electric power, a heat medium controllerthat controls a supply rate of the heat medium supplied to the heatsource equipment, a low-temperature flow controller that controls asupply rate of the low-temperature flow supplied to the heat sourceequipment, a prediction device that predicts startup constraints of thesteam turbine from control input variables of the heat medium controllerand the low-temperature flow controller when the steam turbine isstarted, and a control input variables setter that controls the heatmedium controller and the low-temperature flow controller so as toprevent data predictions by the prediction device from exceeding limitvalues of the startup constraints.

In accordance with the present invention, a steam turbine power plantstarts operating very efficiently in an extended control range ofthermal stresses and other startup constraints.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a steam turbine power plantaccording to a first embodiment of the present invention;

FIG. 2 is a flowchart that represents a starting control sequencerelating to the steam turbine power plant according to the firstembodiment of the present invention;

FIG. 3 is a supplemental explanatory diagram of the starting controlsequence relating to the steam turbine power plant;

FIG. 4 is a flowchart that shows details of step S104 in the sequence ofFIG. 2;

FIG. 5 is a schematic block diagram of a steam turbine power plantaccording to a second embodiment of the present invention;

FIG. 6 is a schematic block diagram of a steam turbine power plantaccording to a third embodiment of the present invention;

FIG. 7 is a diagram showing an example of an operating pattern for heatsource equipment; and

FIG. 8 is an explanatory diagram of a method for controlling heat sourceequipment of the steam turbine power plant according to the firstembodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be described usingthe accompanying drawings.

First Embodiment 1. Steam Turbine Power Plant

FIG. 1 is a schematic block diagram of a steam turbine power plantaccording to a first embodiment of the present invention.

The steam turbine power plant shown in FIG. 1 includes heat sourceequipment 1, a steam generator 2, a steam turbine 3, an electricgenerator 4, a heat medium flow controller 12, a low-temperature fluidflow controller 14, and a steam turbine starting control device 21. Anexample in which the heat source equipment 1 in the present embodimentis a gas turbine, that is, the steam turbine power plant is of acombined-cycle type, is described below.

The heat source equipment 1 uses the amount of heat possessed by a heatmedium (in the present example, a gas fuel, a liquid fuel, ahydrogen-containing fuel, or the like), to heat a low-temperature flow(in the example, a flow of air burned with the fuel) and supply thisheated flow as a high-temperature flow of fluid (in the example, acombustion gas that has been used to drive the gas turbine) to the steamgenerator 2. The steam generator 2 (in the present example, a waste heatrecovery boiler) heats feed water by heat exchange with the heat held bythe high-temperature fluid flow which has been generated by the heatsource equipment 1, and thereby generates steam. The steam thusgenerated by the steam generator 2 is next used to drive the steamturbine 3. The electric generator 4 is coaxially coupled to the steamturbine 3, and the generator 4 converts rotational driving force of thesteam turbine 3 into electric power. The electric power that thegenerator 4 has generated is output to, for example, an electric powersystem (not shown).

The heat medium flow controller 12 (in the present example, a fuelcontrol valve) is provided on a heat medium supply route leading to theheat source equipment 1, and the heat medium flow controller 12 controlsa flow rate of the heat medium supplied to the heat source equipment 1.The low-temperature fluid flow controller 14 (in the present example,IGV) is provided on a low-temperature fluid supply route leading to theheat source equipment 1, and the low-temperature fluid flow controller14 controls a flow rate of the low-temperature fluid supplied to theheat source equipment 1. The controllers 12, 14 are each fitted with acontrol input variables measuring instrument 11 or 13, by which ismeasured a control input variable (in the present example, a valveopening angle) of the controller 12, 14. The control input variable ofthe controller 12, 14 that the control input variables measuringinstrument 11, 13 has measured is input to the steam turbine startingcontrol device 21.

2. Steam Turbine Starting Control Device

The steam turbine starting control device 21 includes a predictiondevice 22, a control input variables setter 23, and control signaloutput devices 24, 25. These elements are described in order below.

(1) Prediction Device

During the startup of the steam turbine 3, the prediction device 22predicts, from the control input variable of the controller 12, 14,future values of the startup constraints estimated to be imposed uponthe steam turbine 3 when a preset time period elapses from the currenttime of day, and outputs the predicted values to the control inputvariables setter 23 (in the present example, a gas turbine controller).The preset time period here refers to a prediction period (describedlater herein) or a period that has been set to be longer than theprediction period. The startup constraints refer to those changes inphysical quantities due to abrupt increases in steam temperature, steampressure, or the like, that will appear when the steam turbine 3 isstarted. The physical quantities are a magnitude of a thermal stressapplied to a turbine rotor of the steam turbine 3, that of axialdifferential thermal expansion in the turbine rotor and a casingaccommodating the turbine rotor, and other variables developing duringthe start of the turbine. Hereinafter, when the wording “thermal stress”is used, this simply means the thermal stress upon the turbine rotor,and when the wording “differential thermal expansion” is used, thissimply means the axial differential thermal expansion of the turbinerotor and the casing.

The startup constraints computed by the prediction device 22 include atleast one of the thermal stress and differential thermal expansion ofthe steam turbine 3 that appear during the prediction period. Theprediction of the thermal stress, in particular, is described below byway of example in the present embodiment. In addition, the predictionperiod is a time that includes a response time from a start ofcontrolling the controller 12, 14 and imparting a change to the amountof heat that the heat source equipment 1 generates, until the steamturbine 3 has suffered a change in startup constraint. That is to say,the prediction period is the response time or a time that has been setto be longer than the response time. The prediction period differsaccording to the kind of startup constraint. For example, a timerequired for a thermal stress to start changing for a reason such as adelay in heat transfer is shorter than a time required for differentialthermal expansion to start developing for a reason such as the delay inheat transfer.

Startup constraints can be calculated in accordance with the known rulesof thermodynamics and/or the rules of heat transfer engineering.Thermal-stress calculation sequences that the prediction device 22executes are set forth below by way of example.

Sequence A1

The control input variable of the controller 12, 14 corresponds to thesupply rates of the heat medium and low-temperature fluid to the heatsource equipment 1 and is therefore closely related to a thermal loadstate of the heat source equipment 1. Accordingly, first a process inwhich heat and matter propagate from the heat source equipment 1 throughthe steam generator 2 to the steam turbine 3 is calculated from thecontrol input variable of the controller 12, 14 that the control inputvariables measuring instrument 11, 13 has measured. Next, a flow rate,pressure, temperature, and other plant physical quantities of the steamthat are estimated to be reached at an entrance of the steam turbine 3after the preset time period has elapsed are further calculated from aresult of that calculation. Predictive computation of the plant physicalquantities can be conducted by first assuming that current change ratesof the heat medium flow rate and the low-temperature fluid flow rate(i.e., change rates of the control input variable of the controller 12,14) remain invariant from the current time to the preset time period,then calculating, from the value measured by the control input variablesmeasuring instrument 11, 13, a value that the control input variable ofthe controller 12, 14 is estimated to take after the elapse of thepreset time period, and computing the plant physical quantities from thecalculated value of the control input variable in the manner describedabove.

Sequence A2

Next on the basis of the calculation results in sequence A1, pressures,temperatures, heat transfer coefficient, and other variables at variousstages of the steam turbine 3 are calculated allowing for a pressuredrop at a first stage of the steam turbine 3.

Sequence A3

Heat transfer of the steam to the turbine rotor is calculated from thecalculation results in sequence A2, and after that, a temperaturedistribution in a radial direction of the turbine rotor is calculatedfrom a result of that calculation.

Sequence A4

Finally, a thermal stress estimated to occur after the elapse of thepreset time period is calculated from the calculation result in sequenceA3, pursuant to the rules of materials engineering that use acoefficient of linear expansion, Young's modulus, Poisson ratio, and/orthe like.

The prediction device 22 executes the above sequences to compute startupconstraints at a predetermined sampling cycle, then store the computedstartup constraints, and output prediction time periods of time-seriesdata to the control input variables setter 23 for each prediction timeperiod.

(2) Control Input Variables Setter

The control input variables setter 23 calculates control input variablesof the controller 12, 14 so that the data predictions that have beeninput from the prediction device 22 fall within a range of the limitvalues which have been set beforehand in the process of starting thesteam turbine 3. These control input variables are calculated fromdeviations between the limit values and a predicted value (e.g., a peakvalue) of the startup constraints time-series data that has been inputfrom the prediction device 22, and the calculations are conducted sothat, for example, the predicted value does not overstep or approach thelimit values. The control input variables to reach the heat medium flowcontroller 12 are output to the control signal output device 24 inadvance, and the control input variables to reach the low-temperaturefluid flow controller 14 are output to the control signal output device25 in advance.

(3) Control Signal Output Devices

The control signal output device 24 computes a command value addressedto the heat medium flow controller 12, from the control input variablesthat the control input variables setter 23 has calculated, and outputsthe computed command value to the heat medium controller 12. The commandvalue to the heat medium controller 12 is determined by numericallyrepresented device characteristics. In the present embodiment, thecommand value is calculated from a fuel flow rate that satisfies a gasturbine load command (MWD), for example. After the command value hasbeen output, the heat medium controller 12 executes PID control so thatthe control input variable measured by the control input variablesmeasuring instrument 11 will be controlled to approach a target value(set point) of the control input variable.

The control signal output device 25 computes a command value addressedto the low-temperature fluid flow controller 14, from the control inputvariables that the control input variables setter 23 calculated, andoutputs the computed command value to the low-temperature fluid flowcontroller 14. The command value to the low-temperature fluid flowcontroller 14 is also determined by the numerically represented devicecharacteristics. In the present embodiment, the command value iscalculated from an air flow rate that satisfies a gas turbine speedcommand, for example. After the command value has been output, thelow-temperature fluid flow controller 14 executes PID control so thatthe control input variable measured by the control input variablesmeasuring instrument 13 will be controlled to approach a target value(set point) of the control input variable.

3. Starting Control Sequence

FIG. 2 is a flowchart representing a starting control sequence that thesteam turbine starting control device 21 conducts for the steam turbine3, and FIG. 3 is a supplemental explanatory diagram of the startingcontrol sequence.

Steps S101 to S103

Steps S101 to S103, shown in FIG. 2, constitute a startup constraintsprediction data-sampling sequence that the prediction device 22executes. That is to say, the steam turbine starting control device 21starts the data-sampling sequence to start the steam turbine 3, andafter this, the controller 21 activates the prediction device 22 tocompute the plant physical quantities that the plant is estimated tohave after the elapse of the preset time period (step S101), and thencompute startup constraints from the computed plant physical quantities(step S102). The plant physical quantities computation sequence and thestartup constraints computation sequence are as described above. Inaddition, since the present embodiment assumes that as described above,the control input variable of the controller 12, 14 changes at a currentrate of change within the preset time period to ensure a lighterprocessing load, the startup constraints are calculated assuming suchlinear changes in startup constraint (in the present example, thermalstress) 201 that are shown in FIG. 3.

After the calculation of the startup constraints, the prediction device22 determines whether the prediction period has passed from the start ofthe steam turbine (step S103), and next until the prediction period haspassed, repeats steps S101-S103 to sample computed startup constraintvalues at fixed cycles (processing cycles of steps S101-S103). After thesampling of the computed startup constraint values corresponding to theprediction period, the steam turbine starting control device 21 shiftssequence control to steps S104 to S107.

Steps S104 to S107

Steps S104 to S107 constitute a sequence that the control inputvariables setter 23 executes, and this sequence is a control sequenceexecuted for the controller 12, 14.

In step S104, the control input variables of the controllers 12, 14 arecomputed from the prediction period of predicted startup constraintstime-series data that was obtained in the sampling sequence of stepsS101-S103. In step S105, command values are output to the controllers12, 14 via the control signal output devices 24, 25 and thecorresponding control input variables of the controllers 12, 14 arecorrected. In the present embodiment, as indicated by an arrow 202 inFIG. 3, a time 203 at which the command values are output to thecontrollers 12, 14 in step S105 is short relative to the predictionperiod, only occupying an initial certain time of the prediction period(this certain time is hereinafter referred to as the control inputupdate interval). A plurality of programs to execute here the sequenceshown in FIG. 2 are active at cycles of the control input updateinterval, with time differences. Accordingly the command values arenewly imparted to the controllers 12, 14 at the cycles of the controlinput update interval by the programs active with the time differences.Thus the command values based on the predicted startup constraints datacorresponding to the prediction period longer than a response time ofthe startup constraints are imparted to the controllers 12, 14 at acycle shorter than the prediction period. If the number of programswhich execute the sequence of FIG. 2 with the time differences is takenas A, the prediction period equals a value obtained by multiplying thecontrol input update interval by A, so this enables overlapped output ofthe same command value to be avoided while ensuring continuity of theoutput of the command values.

After the output of the command signals to the controllers 12, 14,whether startup completion conditions are satisfied is determined instep S106. If the conditions are satisfied, the sequence in FIG. 2 iscompleted, and if the conditions are not satisfied, sequence control isreturned to a very beginning (START) of the starting control sequence,as shown in FIG. 2. The startup completion conditions here areconditions that become a basis for determining whether the steam turbinepower plant has shifted to rated operation (e.g., whether the fuel flowrate, the turbine output, the generator output, and the like havereached respective ratings), and these conditions are defined on aplant-specific basis. This means that up until the startup completionconditions have been satisfied, that is, during the starting controlsequence, the steam turbine starting control device 21 will execute thesequence of FIG. 2 at the cycle of the prediction period.

Look-ahead control of the physical quantities of the steam generated bythe steam generator 2 will be conducted by repeated execution of theabove sequence.

4. Control Input Variables Computation Sequence

FIG. 4 is a flowchart that shows details of step S104 in the sequence ofFIG. 2.

In the flowchart of FIG. 4, whether the startup constraints are lessthan respective threshold values (set points) is determined first (stepS104 a). Each of the threshold values differs according to the kind ofstartup constraint, and is a value that has been set to be smaller thana corresponding limit value, for example, a value of 90% of the limitvalue. If the startup constraints are less than the threshold values,the control input variables of the controllers 12, 14 are set toincrease the flow rates of the heat medium and the low-temperature fluid(steps S104 b, 104 c). If the startup constraints are equal to orgreater than the threshold values, the control input variables of thecontrollers 12, 14 are set to reduce the flow rate of the heat medium(step S104 d) and maintain that of the low-temperature fluid (step S104e). Based on differences between, for example, the peak values and limitvalues (set points for each startup constraint) of the time-series dataobtained within the prediction period, control input variables are setso that the startup constraints occurring after the elapse of the presettime period will fall within the ranges of the limit values. Afterexecution of steps S104 b, S104 c or steps S104 d, S104 c, step S104 isfinished and then control is shifted to step S105. Order of execution ofsteps S104 b, S104 c may be reversed. The same also applies to stepsS104 d, S104 e.

5. Beneficial Effects

The present embodiment yields the following beneficial effects.

(1) Rapid Start of the Steam Turbine

In accordance with the present embodiment, the amount and temperature ofsteam generated by the steam generator 2 can be controlled bycontrolling at least one of the flow rates of the heat medium andlow-temperature fluid supplied to the heat source equipment 1, anelement provided at a front stage of the steam generator 2. For example,the steam temperature can be mainly controlled by operating the heatsource flow controller 12 and controlling the flow rate of the heatmedium. This is because the steam temperature changes with a temperatureof a high-temperature fluid supplied to the steam generator 2.Additionally, the flow rate of the steam can be mainly controlled byoperating the low-temperature fluid flow controller 14 and controllingthe flow rate of the low-temperature fluid. This is because controllingthe flow rate of the low-temperature fluid controls that of thehigh-temperature fluid, hence changing the amount of steam generated inthe steam generator 2.

Thus, the flow rate and temperature of the steam that are the physicalquantities closely associated with the startup constraints such as athermal stress and differential thermal expansion can both be regulated.This in turn enables the steam flow and the steam temperature to becontrolled flexibly according to a particular state of the steam turbine3, and thus allows the steam turbine 3 to be started rapidly in anappropriate way.

In addition, since the amount of steam generated can itself beincreased, a starting time of the steam turbine can be reduced relativeto a conventional configuration in which a flow rate of steam which hasalready been generated in a steam generator is controlled by a controlvalve and then the flow rate of the steam supplied to a steam turbine isregulated. In the conventional configuration, the flow rate of the steamis limited to a narrow regulating range, so while the flow of the steammight be capable of being throttled down with the control valve, theflow rate of the steam cannot be increased.

(2) Suppressed Energy Loss

In the present embodiment, since the amount of steam generated in thesteam generator 2 can itself be controlled, the steam temperature andthe amount of steam generated can be controlled flexibly in response tooperating conditions. This enables energy loss to be suppressed relativeto the conventional configuration in which a surplus of the steam whichhas already been generated is given away via a bypass valve forregulated steam flow.

(3) Highly Efficient and Accurate Predictive Calculation

In a case of a general configuration in which a thermal stress and thelike are predicted and a supply rate of steam supplied to a steamturbine is controlled with a control valve, predictive calculation isusually executed in a plurality of patterns for one output operation ona command value for an opening angle of the control valve. Thiscalculation method is intended to raise adequacy of control by adoptingpredictive calculation results of the patterns as a choice or option.This method, however, applies an extremely significant calculation loaddue to executing the predictive calculation of the patterns, makes itabsolutely necessary to impart a margin to a calculation capacity of acontrol panel or switchboard so that the predictive calculation followsa change in startup constraint, and/or requires a high level of know-howfor construction of an algorithm for increasing a calculation speed.

In a case of the present embodiment, on the other hand, fasterpredictive calculation can be implemented by limiting a transitionassumed of the change rates of the values measured by the control inputvariables measuring instruments 11, 13, to one pattern, and applyingthis pattern to the predictive calculation only. As a result, a samplingperiod at which the predicted values of the plant physical quantitiescan be enhanced and the control input variables can be correspondinglycontrolled more frequently. This provides high prediction accuracy, andyet suppresses calculation throughput, so reducing restrictions on amemory, clock frequency, and other factors of a control panel orswitchboard. High contribution to application and operation of aneasy-to-mount and stable actual machine is anticipated as well.Furthermore, if a time longer than the response time of the startupconstraints is set as the prediction period, this improves predictionaccuracy of the intended startup constraints.

Second Embodiment

FIG. 5 is a schematic block diagram of a steam turbine power plantaccording to a second embodiment of the present invention. In thefigure, substantially the same elements as in the first embodiment areeach assigned the same reference number as on the shown drawings, anddescription of these elements is omitted herein.

As shown in FIG. 5, the present embodiment differs from the firstembodiment in that the former includes a function that corrects thepredicted values of the plant physical quantities. To be more specific,the steam turbine power plant shown in the figure includes a pressuregauge 15 and a temperature gauge 16 on a steam line connecting the steamgenerator 2 and the steam turbine 3. The pressure and temperature of thesteam supplied to the steam turbine 3 are measured by the pressure gauge15 and the temperature gauge 16, respectively, and then input with thevalues measured by the control input variables measuring instruments 11,13 to the prediction device 22. The prediction device 22 then uses themeasurements by the pressure gauge 15 and the temperature gauge 16 tocorrect the plant physical quantities that have been predicted from thevalues measured by the control input variables measuring instruments 11,13.

During plant operation, for example, a certain correlation is likely tooccur between the predicted values and measured values of the steampressure and the steam temperature. For example, the predicted value maybe calculated as a certain level higher or lower than the measuredvalue. Such a correlation is stored as a relational expression or atable in a data storage region of the prediction device 22. When theprediction device 22 conducts a predictive calculation of the plantphysical quantities in accordance with sequence A1, the predicted valuesthat have been calculated from the values measured by the control inputvariables measuring instruments 11, 13 are corrected on the basis of thevalues measured by the pressure gauge 15 and the temperature gauge 16.The prediction device 22 conducts the correction in accordance with theabove correlation. After the correction, the device 22 executessequences A2-A4 and calculates the predicted values of the startupconstraints on the basis of the plant physical quantities obtained afterthe correction.

All other factors, including the configuration and the controlsequences, are substantially the same as in the first embodiment.

The present embodiment yields substantially the same beneficial effectsas those of the first embodiment. In addition, enhancing the accuracy ofthe predicted values of the plant physical quantities by the correctionalso improves the prediction accuracy of the startup constraints andensures adequate starting control of the steam turbine 3.

While an example of correcting the predicted values of both the steamtemperature and the steam pressure has been described in the presentembodiment, the pressure gauge 15 and the temperature gauge 16 may beomitted to correct only one of the two values.

Third Embodiment

FIG. 6 is a schematic block diagram of a steam turbine power plantaccording to a third embodiment of the present invention. In the figure,substantially the same elements as in the first and/or second embodimentare each assigned the same reference number as on the shown drawings,and description of these elements is omitted herein.

The present embodiment differs from the first and second embodiments inthat operation depends upon an operation mode of the heat sourceequipment 1. More specifically, a control input variables setter 26 inthe present embodiment has a command hold function, that is, when theload (gas turbine load) upon the heat source equipment 1 reaches apreset load value (e.g., a load value predefined during plant operationplanning), command values addressed to the controllers 12, 14 are heldfor a fixed time by the above hold function of the setter 26.

In general, a plurality of specific bands on which the load is to beheld are set for the gas turbine and this load often needs to be heldfor a preset time with each arrival of the load at one of the bands.When a power plant equipped with a gas turbine having such anoperational restriction is started, load hold and a load change arerepeated as shown in FIG. 7. The present embodiment is geared to such arestriction on a starting control method.

FIG. 8 is an explanatory diagram of a method for controlling the heatsource equipment 1 by use of the control input variables setter 26.

During the starting control sequence, the control input variables setter26 computes the load of the heat source equipment 1. The heat sourceload 1 can be computed from the heat source flow rate (the valuemeasured by the heat source flow controller 12) and/or the like. Thecontrol input variables setter 26 determines at all times whether theload of the heat source equipment 1 has reached any one of various loadset points, and if the load of the heat source equipment 1 has reachedone of the load set points and needs to be held for operational reasons,the setter 26 sets a load hold time as shown in an example of FIG. 8A.For example, when a difference derived by subtracting a peak value of apredicted thermal stress from a thermal stress limit value is expressedas AG, if AG in the example of FIG. 8A is a plus value, the load holdtime is set to be shorter with greater AG, and if AG is a minus value,the load hold time is set to be longer with greater Δσ. Additionally,the control input variables setter 26 outputs the current control inputvariables as target values to the control signal output devices 24, 25without depending upon the predicted values that are input from theprediction device 22. After that, the setter 26 holds the settings ofthe target control input variables until the preset time has passed.After the preset time has passed, control is shifted to variable controlof the load of the heat source equipment 1. When the operation state ofthe heat source equipment 1 is a load change, the control inputvariables setter 26 executes the variable control of the load of theheat source equipment 1 without executing the control input variableshold sequence described above.

When the control input variables setter 26 executes the variable controlof the load of the heat source equipment 1, the setter 26 sets a loadchange rate command value (control input variables) as shown in FIG. 8B,and outputs the command value to the control signal output devices 24,25. For example, if the value of AG is plus, the load change rate is setto be greater according to the particular value of AG, and if the valueof AG is minus, the load change rate is set to be smaller according tothe value of AG. When the load of the heat source equipment 1 reachesanother set point as a result of such variable control, the preset timeis held once again and the control of the control input variables isreturned to variable control.

Thus, even if the heat source equipment 1 has operational restrictionson the transition of the load, the present embodiment providessubstantially the same beneficial effects as those of the first andsecond embodiments.

Other Examples

While examples of calculating a thermal stress as a startup constraintwith the prediction device 22 have been described in the first to thirdembodiments, differential thermal expansion or both of a thermal stressand differential thermal expansion may be calculated as a control inputvariable(s). Examples of calculation sequences relating to thecalculation of differential thermal expansion are shown as sequences B1to B5 below.

Sequence B1

The flow rate, pressure, temperature, and other factors of the steamthat are estimated to be reached at the entrance of the steam turbine 3after the preset time period has elapsed are calculated in substantiallythe same manner as that of thermal stress calculation.

Sequence B2

On the basis of calculation results obtained in sequence B1, thepressures, temperatures, heat-transfer coefficients, and other factorsof various sections of the turbine rotor and the casing are calculatedallowing for pressure drops at the various sections of the turbine rotorand the casing.

Sequence B3

Temperatures of various sections of the turbine rotor and casing as cutin an axial direction of the turbine are calculated by heat-transfercalculation based on results of the calculation in sequence B2.

Sequence B4

The amounts of axial thermal change (expansion) of the turbine rotor andcasing are calculated from results of the calculation in sequence B3.

Sequence B5

On the basis of calculation results obtained in sequence B4,differential thermal expansion of the turbine rotor and casing after theelapse of the preset time period is calculated in accordance with, forexample, the rules of materials engineering that uses a coefficient oflinear expansion.

In addition, while a combined-cycle power plant has been taken by way ofexample, the present invention can be applied to substantially all typesof power plants including steam turbines, represented by steam powerplants and solar thermal power plants. Sequences to be used to startthese power plants are also substantially the same as in theembodiments.

For example, when the present invention is applied to a steam powerplant, coal or natural gas is equivalent to the heat source, air oroxygen to the low-temperature fluid, a fuel control valve to thecontroller 12, 14, a boiler furnace to the heat source equipment 1, acombustion gas to the high-temperature fluid, a boiler heat transfersection (steam-generating section) to the steam generator 2, and aboiler load controller to the control input variables setter 2.

For example, when the present invention is applied to a solar thermalpower plant, solar light is equivalent to the heat source, aheat-collecting panel drive to the heat medium flow controller 12, aheat-collecting panel to the heat source equipment 1, a heat-collectingpanel direction/angle measuring instrument to the control inputvariables measuring instrument 11, an oil, a high-temperature solventsalt, or any other appropriate solar-energy conversion and hold mediumto the low-temperature fluid and the high-temperature fluid, an oil flowcontrol valve to the low-temperature fluid flow controller 14, and acontrol input variables setter to the control input variables setter 23.

Alternatively, the steam pressure, steam temperature, and fuel flow ratethat are entered in a predictive calculation method 32 may only bereplaced by steam pressure or steam temperature and a predictivecalculation of a thermal stress may be conducted.

Furthermore, the plant physical quantities may include a temperature,pressure, flow rate of exit steam as well as those of entrance steam,the steam flowing into the steam turbine 3. Increasing the number ofkinds of information about the plant physical quantities allows startupconstraint prediction accuracy to be improved. Besides, while the valuesmeasured by the control input variables measuring instruments 11, 13have been adopted as the control input variables of the controllers 12,14 that are to be used for the predictive calculation of the startupconstraints, those measured values may instead be replaced by thecommand values that are output to the controllers 12, 14.

What is claimed is:
 1. A steam turbine power plant, comprising: heatsource equipment that heats a low-temperature flow by applying a heatmedium to generate a high-temperature flow; a steam generator thatgenerates steam using the high-temperature flow generated by the heatsource equipment; a steam turbine driven by the steam generated by thesteam generator; an electric generator that converts rotational motivepower of the steam turbine into electric power; a heat medium controllerthat controls a supply rate of the heat medium supplied to the heatsource equipment; a low-temperature flow controller that controls asupply rate of the low-temperature flow supplied to the heat sourceequipment; a prediction device that predicts startup constraints of thesteam turbine from control input variables of the heat medium controllerand the low-temperature flow controller when the steam turbine isstarted; a control input variables setter that sets the control inputvariables of the heat medium controller and the low-temperature flowcontroller from limit values of the startup constraints as well as froma value predicted by the prediction device; and a control signal outputdevice that outputs command values to the heat medium controller and thelow-temperature flow controller in response to the control inputvariables.
 2. The steam turbine power plant according to claim 1,wherein the prediction device computes at least one of a thermal stressand differential thermal expansion of the steam turbine that occurduring a previously set prediction time period, as a predicted value ofthe startup constraints.
 3. The steam turbine power plant according toclaim 2, wherein the prediction time period is set to be long withrespect to a response time of the startup constraints relative tocontrol of the heat source equipment.
 4. The steam turbine power plantaccording to claim 1, further comprising: a measuring instrument thatmeasures at least one of a pressure and temperature of the steamsupplied to the steam turbine; wherein correction of a predicted valueof the startup constraints is based upon a value measured by themeasuring instrument.
 5. The steam turbine power plant according toclaim 1, wherein: the heat source equipment is a gas turbine, the heatmedium is a fuel, and the low-temperature flow is a flow of air.
 6. Thesteam turbine power plant according to claim 5, wherein: when a loadvalue of the gas turbine equals a previously set point, the controlinput variables setter holds for a previously set time the commandvalues that are output to the heat medium controller and thelow-temperature flow controller.